1. Field of the Invention
The present invention is in the field of passivation of semiconductor devices generally, and specifically in the field of glass passivation of p-n junctions.
2. Description of the Prior Art
P-N junctions have been passivated with organic materials such as silicone resins, silicone varnishes and silicone rubbers. In some cases these organic coatings contained fillers, usually metallic particles.
The organic coatings in general were not totaly stable, especially at elevated temperatures to be considered reliable.
Thin glass coatings, having a thickness of from about 5.mu. to 20.mu., have been used and were in general more stable than the organic coatings. However, such thin glass coatings are not entirely satisfactory because ions of heavy metals adhere to the glass coating and the thin glass coatings themselves react with hydrogen gas in furnaces used to braze the glass coated wafer to metallic bases.
Both of these occurrences lead to deterioration of the electrical characteristics of the semiconductor device.
It is known that the effect of the ions of heavy metals on the electrical characteristics of the device and the reaction of the glass coating with the hydrogen gas in the brazing furnace can be reduced to an acceptable degree if a thick glass coating, as for example a glass coating having a thickness of from 30.mu. to 50.mu. is employed.
However, at this thickness, the mismatch in thermal expansion between the glass coating and the semiconductor material causes the glass coating to crack and the electrical characteristics of the semiconductor device deteriorate.